The chemical structure of the molecules
results in 75 chlorinated naphthalene congeners. The
physical and chemical properties are dependent on the
degree of chlorination. Whereas the melting and boiling
point increase with an increase in the number of chlorine
atoms, there is a simultaneous reduction in vapour
pressure and water solubility.

ORIGIN AND USE

Usage:
Chlorinated naphthalenes are used in the electrical industry and
as additives. Only isomeric mixtures characterised by their
chlorine content are commercially available.

Origin/derivation:
The substances are not found naturally. They are obtained by
batchwise chlorination of naphthalene in the presence of ferric
chloride as a catalyst.

Production figures:Worldwide approximately 5,000 t per annum with a declining
tendency (acc. KOCH, 1989).

Toxicity

Humans:

TCLo 30 mg/m3, inhalation
(trichloronaphthalene)

acc. KOCH, 1989

Mammals:

Rat:

LD50 1,540 mg/kg, oral

acc. KOCH, 1989

LD50 868 mg/kg, oral
(2-chloronaphthalene)

acc. KOCH, 1989

Mouse:

LD50 1,091 mg/kg, oral

acc. KOCH, 1989

LD50 2,087 mg/kg, oral
(2-chloronaphthalene)

acc. KOCH, 1989

Characteristic effects:

Humans/mammals: Poisoning is due to oral application
(foodstuffs) or inhalation. The toxicity is largely governed by
the degree of chlorination. Chloracne and liver damage are
especially caused by pentachloro- and hexachloronaphthalene while
chlorinated naphthalenes with 1 to 3 chlorine atoms hardly have
any toxic effects.

ENVIRONMENTAL BEHAVIOUR

Chlorinated naphthalenes are very resistant to degradation.
Mobility is slight in water and soil, but there is a pronounced
tendency towards bioaccumulation and geoaccumulation depending on
the degree of chlorination. Highly chlorinated naphthalenes are
very persistent. Incomplete combustion results in the formation
of polychlorinated dibenzodioxins and -furans (PCDD/F).

Similarly to chlorinated biphenyls, the toxicity and the
environmental persistence of chlorinated naphthalenes increase
with the degree of chlorination. The use of naphthalene with a
high degree of chlorination should therefore be kept to a
minimum.